Roller shade systems having flexible shades supported by elongated roller tubes are well known. The roller tube, typically made from aluminum or steel, is rotatably supported to provide for winding receipt of the flexible shade on the roller tube. Roller shades include manual shades having spring driven roller tubes and motorized shades having drive motors engaging the roller tube to rotatingly drive the tube. The drive motors for motorized shades include externally mounted motors engaging an end of the roller tube and internal motors that are received within an interior defined by the tube.
Conventional roller shades have support systems that engage the opposite ends of the roller tube to provide the rotatable support that is required for winding and unwinding of the flexible shade. Referring to FIG. 1, for example, there is shown an end portion of a roller tube 2 that is rotatably supported in a conventional manner. The support system, shown schematically in FIG. 1, includes a drive end support assembly having a coupler 3 engaging the open end 4 of the tube 2 for rotation therewith. The coupler 3 is adapted to receive the drive shaft 6 of motor 5 such that rotation of the drive shaft is transferred to the coupler for rotation of the tube 2. As shown, the motor 5 is secured to a bracket 7 for attachment of the roller shade to the wall or ceiling of a structure, for example. A coupler engaging an opposite end of the roller tube (not seen) could receive a motor drive shaft or, alternatively, could receive a rotatably supported shaft of an idler assembly. An example of a roller shade including an end supported tube is shown in U.S. patent application Ser. No. 10/039,818.
A roller shade tube supported in a conventional manner from the opposite ends will deflect in response to transverse loading, from the weight of an attached shade for example, substantially similar to a beam structure having support conditions known as “simple supports”. A simply supported beam is vertically supported but is not restrained against rotation at the support locations. The response of a roller tube, supported at its ends in a conventional manner, to transverse loading is illustrated in FIG. 2. The distance, L, between the support points for the roller tube 8, also known as effective length, is substantially equal to the overall length of the tube. Transverse loading applied to the end-supported roller tube 8, from the weight, W, of a flexible shade 9 as well as from self-weight of the tube, results in a downward “sagging” deflection, d, in a central portion of the roller tube 8 with respect to the supported ends.
For roller shades having wider shades (e.g., widths of 15 to 30 feet or more), support of the correspondingly long roller tubes in a conventional manner can result in sagging deflection detrimental to the appearance of a supported shade. As illustrated in FIG. 2, V-shaped wrinkles, also known as “smiles”, can be formed in an unrolled shade supported by a sagging roller tube. Sagging deflection in a conventionally supported roller tube can also have a detrimental effect on shade operation. During winding of a shade, the shade is drawn onto the tube in a direction that is substantially perpendicular to the axis of the tube. Due to curvature along the length of a sagging tube, opposite end portions of a supported shade will tend to track towards the center portion of the tube as the shade is rolled onto the tube. Such uneven tracking of opposite end portions of the shade can cause the end portions to be wound more tightly onto the end portions of the roller tube than the central portion of the roller tube. As a result, the central portion of the shade is not pulled tightly to the tube causing it to tend to buckle. This buckling of the central portion of the shade, if severe enough, can create variations in radial dimensions of the rolled shade along the length of the tube, thereby impairing subsequent rolling of lower portions of the shade.
Transverse deflection in a simply supported beam will vary depending on the effective length of the beam, the shape and dimensions of the beam cross section and the properties of the material from which the beam is made. For a simply supported beam having a point load, P, applied at the center, the transverse deflection at the beam center will be equal to PL3/48EI, where E is the elastic modulus for the material and I is the modulus of inertia. The modulus of inertia, I, is a function of section geometry and is based on the second moment of area for the beam cross section taken about the centroidal axis. Since deflection increases exponentially (as the cube) with increasing tube length, it is understandable that excessive sagging deflection results when relatively long roller tubes are end-supported in a conventional manner.
The problem of sagging deflection in longer roller tubes has been addressed in prior art roller shades by increasing the diameter of the roller tube. Increase in tube diameter results in a shift of material to a greater distance from the tube centroidal axis such that the modulus of inertia, I, is increased. As shown by the above-discussed equation, sagging deflection in an end supported roller will decrease in direct proportion to increase in the moment of inertia, I. A known roller shade system with shades having a width of 20 feet, for example, includes a correspondingly long roller tube having a diameter of approximately 4¾ inches. Increasing the shade width to 25 feet required that the tube diameter be increased to 6¼ inches to prevent excessive sagging deflection in the roller tube. Increasing the shade width beyond 25 feet required that the roller tube diameter be increased to 8 inches or more.
Although increase of the roller tube diameter serves to reduce sagging deflection in conventional end-supported tubes, there are undesirable consequences associated with such a solution. Increasing the diameter of the roller tube increases weight, thereby potentially affecting the size and type of structure capable of providing rotatable support for the tube. Also, additional space required by the larger diameter roller tube and its associated support structure may not be readily available in many installations.